Memory devices are typically provided as internal, semiconductor, integrated circuits and/or external removable devices in computers or other electronic devices. There are many different types of memory, including random-access memory (RAM), read only memory (ROM), dynamic random access memory (DRAM), synchronous dynamic random access memory (SDRAM), flash memory, and resistance variable memory, among others. Types of resistance variable memory include programmable conductor memory, resistive random access memory (RRAM), phase change random access memory (PCRAM), magnetoresistive random access memory (MRAM; also referred to as magnetic random access memory), and conductive-bridging random access memory (CBRAM), among others.
Memory devices such as resistance variable memory devices may be utilized as non-volatile memory for a wide range of electronic applications in need of high memory densities, high reliability, and low power consumption. Non-volatile memory may be used in, for example, personal computers, portable memory sticks, solid state drives (SSDs), personal digital assistants (PDAs), digital cameras, cellular telephones, portable music players such as MP3 players, movie players, and other electronic devices. Data, such as program code, user data, and/or system data, such as a basic input/output system (BIOS), are typically stored in non-volatile memory devices.
Resistance variable memory such as PCRAM includes memory cells that can store data based on the resistance state of a storage element, e.g., a memory element having a variable resistance. The storage element of a PCRAM cell may comprise a phase change memory material, such as a chalcogenide material, e.g., Germanium-Antimony-Telluride (GST).
As such, resistance variable memory cells, such as PCRAM cells, can be programmed to store data corresponding to a target data state by varying the resistance level of the storage element. One of a number of data states, e.g., resistance states, can be set for a resistance variable memory cell. For example, a single level cell (SLC) may be programmed to one of two data states, e.g., logic 1 or 0, which can depend on whether the cell is programmed to a resistance above or below a particular level. As an additional example, various resistance variable memory cells can be programmed to one of multiple different resistance states corresponding to multiple data states. Such cells may be referred to as multi state cells, multi-digit cells, and/or multilevel cells (MLCs), and can represent multiple binary digits of data, e.g., 10, 01, 00, 11, 111, 101, 100, 1010, 1111, 0101, 0001, etc.
Resistance variable memory cells can comprise a selector device, e.g., a switch, coupled in series with the storage element in a cross-point array structure, for instance. As an example, the storage element can comprise a resistance variable material, e.g., a phase change memory (PCM) material, formed between a pair of electrodes. The storage element can be formed in series with the selector device, which can be a two terminal selector device comprising a selector device material formed between a pair of electrodes. In various instances, an electrode, e.g., a middle electrode, can be shared by the storage element and the selector device. The other two electrodes, between which the selector device material and storage element material are formed, can be coupled to respective conductive lines of the array, e.g., a word line and a bit line. In instances in which a storage element comprising a PCM material is formed in series with a selector device, the array of cells can be referred to as a PCMS (phase change memory/switch) array.